Abstract: A large data set of fundamental mode Rayleigh wave amplitudes is analyzed to derive a new global three-dimensional model of shear wave attenuation in the upper mantle. The amplitude observations span a range of periods between 50 and 250 s and are derived from earthquakes with M W > 6.0 that occurred between 1993 and 2005. Four separate factors may influence an amplitude anomaly: intrinsic attenuation along the raypath, elastic focusing effects along the raypath, uncertainties in the strength of excitation, and uncertainties in the response at the station. In an earlier paper (Dalton and Ekstrm, 2006a), dependence of the retrieved attenuation structure on these terms was shown to be significant and an approach was developed to invert the amplitudes simultaneously for each term. The new three-dimensional attenuation model QRFSI12, which is the subject of this paper, is derived using this method. The model contains large lateral variations in upper-mantle attenuation, 60% to 100%, and exhibits strong agreement with surface tectonic features at depths shallower than 200 km. At greater depth, QRFSI12 is dominated by high attenuation in the southeastern Pacific and eastern Africa and low attenuation along many subduction zones in the western Pacific. Resolution tests confirm that the change in pattern of attenuation above and below 200-km depth can be determined with confidence using the fundamental mode data set. The new model is highly correlated with global models of shear wave velocity, particularly in the uppermost mantle, suggesting that the same factors may control both seismic attenuation and velocity in this depth range. However, forcing the lateral perturbations in attenuation to match those found in global velocity models decreases the data variance reduction, which suggests that subtle differences between patterns of attenuation and velocity are robust.

Abstract: Peridotite xenoliths brought up to the surface by the volcanism of the Kerguelen Islands represent a mantle that has been affected by a high degree of partial melting followed by intense melt percolation above the Kerguelen plume. These xenoliths are therefore particularly suitable to investigate effects of melt-rock interaction on crystallographic fabrics (lattice-preferred orientation (LPO)) of peridotite minerals and on the LPO-induced seismic properties of peridotites above a mantle plume. We have studied a suite of 16 ultramafic samples representative of different degrees of partial melting and magma-rock interaction among which the protogranular harzburgites are the least metasomatised xenoliths and dunites are the ultimate stage of metasomatism. Olivine LPO is characterized by high concentration of [010] axes perpendicular to the foliation and [100] axes close to the lineation or distributed in the foliation plane in harzburgites, whereas the high concentration of [100] axes is parallel to the lineation and [010] axes is perpendicular to the assumed foliation in dunites. Olivine LPO in harzburgites is interpreted as being due to a deformation regime in axial compression or transpression. The fabric strength of olivine decreases progressively from protogranular to poikilitic harzburgites and finally to dunites, for which it remains nevertheless significant (J index $\geq$ 3.8). Seismic properties calculated from LPO of minerals indicate that metasomatism at higher melt/rock ratio lowers the P wave velocities. The most significant difference between harzburgites and dunites corresponds to the distribution of S wave anisotropy. Harzburgites display the maximum of anisotropy within the foliation plane and the minimum of anisotropy perpendicular to the foliation plane, whereas the lowest anisotropy is parallel to the lineation for dunites. These modifications of seismic properties as a result of metasomatic processes may induce seismic heterogeneities in the mantle above the Kerguelen plume. In addition, assuming a lithospheric mantle primarily harzburgitic and structured with a horizontal foliation, the seismic properties calculated for the Kerguelen xenoliths reconcile the rather high anisotropy evidenced by the horizontally propagating surface waves with the apparent isotropy revealed by the absence of splitting of vertically propagating teleseismic SKS waves recorded by the GEOSCOPE Kerguelen station.

Abstract: The high Arctic has the world's simplest terrestrial vertebrate predatorprey community, with the collared lemming being the single main prey of four predators, the snowy owl, the Arctic fox, the long-tailed skua, and the stoat. Using a 20-year-long time series of population densities for the five species and a dynamic model that has been previously parameterized for northeast Greenland, we analyzed the population and community level consequences of the ongoing and predicted climate change. Species' responses to climate change are complex, because in addition to the direct effects of climate change, which vary depending on species' life histories, species are also affected indirectly due to, e.g., predatorprey interactions. The lemmingpredator community exemplifies these complications, yet a robust conclusion emerges from our modeling: in practically all likely scenarios of how climate change may influence the demography of the species, climate change increases the length of the lemming population cycle and decreases the maximum population densities. The latter change in particular is detrimental to the populations of the predators, which are adapted to make use of the years of the greatest prey abundance. Therefore, climate change will indirectly reduce the predators' reproductive success and population densities, and may ultimately lead to local extinction of some of the predator species. Based on these results, we conclude that the recent anomalous observations about lack of cyclic lemming dynamics in eastern Greenland may well be the first signs of a severe impact of climate change on the lemmingpredator communities in Greenland and elsewhere in the high Arctic.

Abstract: An investigation of the presence of influenza A virus has been conducted in king penguins ( Aptenodytes patagonicus ) at the Possession Island in the Crozet Archipelago, Antarctica, using a rapid molecular diagnostic method based on real-time polymerase chain reaction. No evidence of outbreak or positive viral infection of influenza A virus was found in this study. We however recommend the implementation of long-term surveillance in seabird populations of polar ecosystems to detect the potential introduction of exotic strains and potential existence of a local epidemiological cycle for avian influenza viruses.